A magnetic reading converter called a magnetoresistive (MR) sensor or head is conventionally known, where it is know that data with a high linear density can be read out from a magnetic surface. In such a MR sensor, a magnetic signal is detected through a resistance change which is a function of intensity and direction of magnetic flux sensed by a reading element.
The MR sensor is actuated according to anisotropic magnetoresistance (AMR) effect where one component of a resistance in the reading element is varied proportionally to the square of the cosine of an angle formed between the magnetization direction and the direction of sensing current flowing through the element. The AMR affect is detailed in D. A. Thompson et al., "Thin Film Magnetoresistors in Memory, Storage, and Related Applications", IEEE Trans. on Mag., Vol. MAG-11, No.4, pp.1039 to 1050(1975).
Furthermore, a significant magnetoresistance effect is recently reported, where a resistance change of a layered magnetic sensor is attributed to the spin-dependent transmission of conduction electrons between magnetic layers disposed through a non-magnetic layer and the spin-dependent scattering at the interface occurring therewith. This magnetoresistance effect is called `giant magnetoresistance effect`, `spin valve effect`, or the like. Such a magnetoresistive sensor is of a suitable material and has an improved density and a large resistance change as compared with a sensor using the AMR effect. In this kind of MR sensor, in-plane resistance between a pair of ferromagnetic layers isolated by a non-magnetic layer is varied proportionally to the cosine of an angle between the magnetization directions of the two layers.
Japanese patent application laid-open No.2-61572(1990) discloses a layered magnetic structure where a large MR change is given by anti-parallel arrangement of magnetization between magnetic layers. A material available for the layered structure disclosed therein is a transition metal and an alloy for the ferromagnetic layer.
Also, it discloses that a structure where an anti-ferromagneticlayer is added to at least one of two ferromagnetic layers to be separated by an intermediate layer is suitable and the anti-ferromagnetic layer in suitably of FeMn.
Japanese patent application laid-open No.4-358310(1992) disclosed a MR sensor that has two ferromagnetic thin film layers separated by a non-magnetic metal thin film layer, the magnetization directions of the two ferromagnetic thin film layer are orthogonal to each other when applied magnetic field is zero, and a resistance between two non-coupled ferromagnetic layers is varied proportionally to the cosine of an angle formed between the magnetization directions of the two layers and is independent of the direction of current flowing through the sensor.
Japanese patent application laid-open No.8-127864(1996) discloses a magnetoresistance effect device that is composed of several magnetic thin films layered through a non-magnetic layer on a substrate, an anti-ferromagnetic thin film is provided next to one of magnetically soft thin films which are adjacent through a non-magnetic thin film, H.sub.c2 &lt;H.sub.r is given where H.sub.r is a bias magnetic field of the anti-ferromagnetic thin film and H.sub.c2 is coercive force of the magnetically soft thin film, and the anti-ferromagnetic layer is of a superlattice composed of at least two of NiO, Ni.sub.x Co.sub.1-x O, CoO. Also, Japanese patent application laid-open No.9-50611(1997) discloses a magnetoresistance effect device composed of magnetoresistance effect film with the same structure where the anti-ferromagnetic layer is composed of two layer film in which CoO is layered by 10 to 40 .ANG. on NiO.
However, there are several problems with conventional magnetoresistance effect film.
First, a magnetization step of conducting thermal treatment in a magnetic field is needed for the fabrication process of the magnetoresistance effect device since one-directional anisotropy is applied to adjacent magnetic thin films using an anti-ferromagnetic thin film.
Second, the thermal stability of one-directional anisotropy at the working temperature is not good since the one-directional anisotropy is applied to the adjacent magnetic thin films using an anti-ferromagnetic thin film with a relatively low Neel temperature.
Third, device sensitivity or the symmetricalness in device output is deteriorated since the ferromagnetic layers may be magnetostatically coupled when the device is patterned, due to the multilayer structure where the ferromagnetic layers are adjacent through a non-magnetic layer.
Fourth, the ratio of resistance change is lower than that of magnetoresistance effect film called `coupling type` with a multilayer structure since resistance change is basically applied using a variation in mean free path length of conduction electrons in the three layers of magnetic thin film/non-magnetic thin film/magnetic thin film.